Support is requested for a Keystone Symposia meeting entitled Co-Infection: A Global Challenge for Disease Control, organized by Rodrigo Corra-Oliveira, David Dunne and Andrea Graham. The meeting will be held in Ouro Preto, Brazil from March 15-20, 2015. Multi-species co-infections impose one of the greatest challenges to global health and to our efforts to develop effective methods of infectious disease control. Populations living in rural areas of many low-income countries are exposed to both chronic and acute infection with multiple pathogens. In such conditions co-infection is common and the cause of additive or synergistic morbidities. Studying co-infections is difficult and complex as different pathogens may interact in many different ways, either directly or via the host immune response. Indeed, in some contexts, a community of organisms within a host may promote defense against other organisms. This Keystone Symposia meeting will focus on our current understanding of synergism/antagonism among pathogens causing common co-infections. In doing so it will bring together leading researchers and their knowledge of immune responses in co-infected individuals, co-infection immunoepidemiology, modeling of co-infections to predict disease and infection outcomes, and the specific challenges that co-infection presents to vaccine design strategies, and effective application of chemotherapy. This diversity of scientific disciplines will together address the impacts of co-infection, particularlyin the context of the neglected tropical diseases that are prevalent in many low- and middle-income countries. For example, in some of the poorest parts of the world, HIV, TB, leprosy, HTLV, malaria, dengue, and chronic helminth infections are co-endemic. To find the understanding and the means to effectively tackle the diverse clinical and public health problems of co-infection, we need to combine information derived from basic hypothesis-lead research, descriptive epidemiology and new computational modeling techniques. The goal of this symposium will be to broaden and deepen our understanding of within-host and population-level interactions between different co-infecting pathogens and propose appropriate to move towards clinical and public health solutions, including the delivery of effective vaccination and chemotherapy.